An RF-based positioning system is composed of a mobile radio wave receiver and a plurality of radio wave transmitters installed in a space.
In the RF-based positioning system configured as above, the radio wave transmitter transmits a signal to the space periodically and the radio wave receiver receives the signal transmitted by the radio wave transmitter to determine an ID of the radio wave transmitter transmitting the corresponding signal and signal strength. When positional information of the radio wave transmitter is added to the determined results, a position of the radio wave transmitter transmitting the corresponding signal can be calculated by using a triangulation method or the like. For instance, nodes constituting a ZigBee network receive beacon messages periodically to generate a received signal strength indicator (RSSI) list and by applying a calculation method such as a triangulation method based on positional information of nodes transmitting the beacon messages, a relative position of the corresponding terminal node can be calculated from the ZigBee nodes. In this case, if absolute positions of the ZigBee nodes are known, absolute positions of terminal nodes can be also determined.
The RF-based positioning technology has an advantage of easily constructing a system or an environment localizing an object or a person carrying a portable device by using an environment sensor and the simple portable device, but is disadvantageous in that positioning performance is greatly influenced by the surrounding environment. The reason is that the RF radio wave varies greatly in moving direction and strength according to an environmental structure, a physical property of wall, and presence or absence of an obstacle including a person and an object.
In order to overcome the disadvantage, closely disposing a plurality of RF transmitting nodes in a space in a regular pattern such as a grid pattern and constructing an RF Fingerprint for the entire space have been attempted to be used for positioning, but it is difficult to continuously obtain excellent performance due to characteristics of the RF radio wave as described above in the actual environment, and due to installation of a large number of sensors in the environment, commercialization is blocked.
A pyroelectric infrared (PIR) sensor as an on-off sensor outputting a value when movement is sensed in a sensible area is primarily used to sense a moving body and as an example, there is an electric lamp which is automatically turned on and off. The PIR sensor has an advantage of low cost and is advantageous for privacy protection as compared with a camera sensor because when installed in a space, the PIR sensor cannot determine who the sensed movement belongs to and can detect only movement of a person (i.e., the trace of movement), but if several people exist in the space, the PIR sensor cannot distinguish who the sensed movement belongs to.